The three electrical stimulation systems available for treating nonunion of long bones are successful in approximately 85% of cases. The percutaneous direct current bone growth stimulator is partially invasive, allows patient mobility, can be used with magnetic fixation devices, and can be monitored for proper function, but it requires an operation, cannot be used where infection exists, and is subject to breakage. The implantable direct current bone growth stimulator is similar, but is totally invasive. The external pulsing electromagnetic field bone growth stimulator is noninvasive and can be used where infection exists, but it requires long, exact patient compliance and cannot be used with magnetic fixation devices or at certain sites. None of the systems can be used where synovial pseudarthrosis or a sizeable gap between bone ends exists, nor are they more effective than bone grafting. Whether their use might evoke malignant transformation or might accelerate or retard epiphyseal growth patterns is not known. Many controlled studies are needed before it is clear how commonly electrical stimulation should be used to treat bony ununion.